The Pragmatic Craftsman :: Simplicity from complexity : by Stanley Kubasek ::

Do you get notified of every email you receive? You don’t find that distracting? I find it very distracting. I remember receiving emails every couple of minutes at my old job. I finally had to turn off the notification alerts because I could not concentrate on work. At my current job, we use Lotus Notes and though the amount of email is great, I don’t get notifications like you do in Outlook. That helps a lot.

I agree with Jeff Atwood completely:

If you want more productivity: turn off automatic email notification. Concentrate on the thing you’re doing and finish it. Then, check your email.